I'm skinny and i believe to have a fast metabolism, sometimes bettween meals and 3hours w/o eating i start feeling pain in stomach why it happens?

? hunger pangs: I'm not sure if what you are feeling is related to an empty stomach, but in some people--probably especially those who seem to metabolize food efficiently such as yourself--the stomach may have completed its work of digestion in 3 hours and is empty. Associated with hormones triggered by brain signals, the empty stomach contracts which is experienced as "hunger pain" or "hunger pangs."